Vehicles powered by liquid petroleum fuels, such as diesel fuel or gasoline, have fuel systems that typically include fuel filters. The fuel filter operates to minimize the risk that contaminates, such as dirt particles or water, will reach other components of the system where the contaminates may cause damage.
There are many types of fuel filter elements known in the prior art. Some provide only particulate filtration. Others provide filtration and water separation. A popular configuration for fuel filters for larger vehicles includes a stationary head which is connected in the fuel line of the vehicle fuel system. A replaceable element attaches to the head, usually in "spin-on" fashion. The element may be readily replaced periodically to prevent the element from being clogged by contaminates.
In many fuel systems the filter head and element are located between the fuel tank of the vehicle and the fuel pump. In this configuration, the position of the filter minimizes the risks that contaminates will reach the pump.
In conventional fuel system configurations problems sometimes arise when the element is changed. When a new element is installed it is naturally filled with air from the atmosphere. As a result, there is an air pocket in the fuel system between the fuel tank and the pump. The air may cause stalling when it reaches the engine or it may prevent the fuel pump from drawing fuel by vacuum from the tank through the new element.
To minimize this problem, skilled mechanics will attempt to fill a new element with fuel prior to installation. This reduces the size of the air pocket, but creates a possibility of placing contaminated fuel on the "clean" side of the element. The air pocket cannot be eliminated completely, however, because there is always some air filled space in the filter head when the element is replaced. As a result the system may still become inoperative.
In many systems the element is mounted on the head with the open end of the element upwards. In these cases filling the element with fuel prior to installation is fairly effective. In other systems the filter head is mounted so that the element is installed with its open end sideways or down. In these configurations it is virtually impossible to install the element in a filled condition and the size of any air pocket, and the possibility of a problem when the element is changed, is increased.
Air can also enter the element when water is drained from a contaminant collection chamber in the lower portion of the element. This air can cause problems similar to those associated with changing the filter.
To deal with this problem, manufacturers of filters have developed filter heads that include priming pumps. These pumps typically use manual pumping action to draw fuel from the tank into the filter head. The priming pump is then used to fill the new element with fuel and to force the air pocket out of the filter and/or downstream of the fuel pump. This insures that there are no significant air pockets between the fuel tank and the pump that could prevent fuel flow by suction.
Manufacturers of filter heads which include priming pumps have taken two approaches. The first approach is to place a pump directly in the fuel path between the fuel inlet to the head and the element. This approach typically involves use of a plunger type pump with check valves on each side to assure one way flow. The problem with this approach is that the check valves in the fuel flow path are restrictions that limit the rate of fuel flow when the vehicle is in normal operation.
An alternative approach has been to provide two separate flow paths through the filter head and to include in the head a manual valve that allows the operator to select the flow path. When it is necessary to prime the system, a flow path which includes the pump and check valves is selected. The pump is then used to fill the element and the line with fuel. Once this is done the condition of the valve is manually changed. The fuel then flows directly through the filter head to the in-flow area of the element, and fuel no longer flows through the priming pump and check valves. This eliminates the restriction.
A problem with the approach of providing two flow paths through the filter head and a manual valve, is that the operator must manually change the condition from the normal operating mode to the priming mode and back again. This is inconvenient, time consuming, and presents opportunities for mistakes. The use of a manual valve mechanism also adds cost to the filter head and is an area of possible mechanical failure.
Thus, there exists a need for a filter head that incorporates a priming pump that is easier to operate, reliable, and economical to manufacture.